Halftone phase shift mask blank, halftone phase shift mask, and method of producing the same

ABSTRACT

A halftone phase shift mask blank for use in manufacturing a halftone phase shift mask comprises a transparent substrate, a light transmitting portion formed on the substrate for transmitting an exposure light beam, a phase shifter portion formed on the substrate for transmitting a part of the exposure light beam as a transmitted light beam and for shifting a phase of the transmitted light beam by a predetermined amount, and a phase shifter film for forming the phase shifter portion. The halftone phase shift mask has an optical characteristic such that light beams passing through the light transmitting portion and through the phase shifter portion cancel each other in the vicinity of a boundary portion therebetween, thereby maintaining and improving an excellent contrast at a boundary portion of an exposure pattern to be transferred onto the surface of an object to be exposed. The phase shifter film comprises a film containing silicon, oxygen, and nitrogen as main components and an etching stopper film formed between the film and transparent substrate.

This is a divisional of application Ser. No. 10/370,776 filed Feb. 24,2003 now U.S. Pat. No. 7,115,341. The entire disclosure(s) of the priorapplication(s), application number(s) 10/370,776 is hereby incorporatedby reference.

BACKGROUND OF THE INVENTION

The present invention relates to a halftone phase shift mask blank, ahalftone phase shift mask, and a method of producing the same and,particularly, to a halftone phase shift mask blank suitable for use in anext-generation short-wavelength exposure light source such as an ArFexcimer laser (193 nm) and an F₂ excimer laser (157 nm).

For a dynamic random access memory (DRAM), mass production of 256 Mbitproducts has been established at present and a higher integration from aMbit level to a Gbit level is making a progress. Following thedevelopment of higher integration, a design rule of an integratedcircuit becomes finer. It is only a matter of time before a fine patternwith a line width (half pitch) of 0.10 μm or less is required.

As one approach to adapt for miniaturization of the pattern, aresolution of the pattern has been improved by shortening a wavelengthof an exposure light source. As a result, a KrF excimer laser (248 nm)and an ArF excimer laser (193 nm) are mainly used as the exposure lightsource in the existing photolithography.

Although the shortened exposure wavelength improves the resolution, thedepth of focus becomes shallow. This results in adverse influences, suchas an increase in load imposed on a design of an optical systemincluding a lens and decrease in stability of a process.

In order to solve the above-mentioned problems, a phase shift method hasbecome used. In the phase shift method, a phase shift mask is used as amask for transferring the fine pattern.

The phase shift mask comprises, for example, a phase shifter portionwhich forms a patterned portion on the mask, and an unpatterned portionin which the phase shifter portion does not exist. With this structure,light beams transmitted through both of the phase shifter portion andthe unpatterned portions are shifted in phase by 180° with respect toeach other to cause mutual interference of the light beams in a patternboundary area. In this manner, contrast of a transferred image isimproved.

It is known that a phase shift amount φ (rad) of the light beam passingthrough the phase shifter portion depends on a real part n of a complexrefractive index and a film thickness d of the phase shifter portion andthat the relationship given by the following equation (1) isestablished.φ=2πd(n−1)/λ  (1)

Here, λ denotes a wavelength of an exposure light beam. Therefore, inorder to shift the phase by 180°, the film thickness d is given by:d=λ/{2(n−1)}  (2)The above-mentioned phase shift mask achieves an increase in depth offocus sufficient to obtain a desired resolution. It is thereforepossible to improve both of the resolution and the applicability of theprocess without changing the exposure wavelength.

Practically, the phase shift mask is generally classified into a perfecttransmission (Levenson type) phase shift mask and a halftone phase shiftmask in accordance with a light transmission property of the phaseshifter portion forming the mask pattern. In the former, the phaseshifter portion has a light transmittance equivalent to that of theunpatterned portion (light transmitting portion). Thus, the former is amask substantially transparent to the exposure wavelength and isgenerally effective in transfer of a line and space pattern.

On the other hand, in the latter, i.e., the halftone type, the phaseshifter portion (light semi-transmitting portion) has a lighttransmittance on the order of about several percentages to several tensof percentages of that of the unpatterned portion (light transmittingportion). It is understood that this type is effective in preparation ofa contact hole or an isolated pattern.

The halftone phase shift mask includes a double-layer type halftonephase shift mask comprising a layer for mainly adjusting thetransmittance and another layer for mainly adjusting a phase; and asingle-layer type halftone phase shift mask which is simple in structureand easy in manufacture.

At present, the single-layer type is a mainstream because it is easy inprocessing. In most cases, the halftone phase shifter portion comprisesa single-layer film of MoSiN or MoSiON.

On the other hand, in the double-layer type, the halftone phase shifterportion comprises a combination of the layer for mainly controlling thetransmittance and the layer for mainly controlling the phase shiftamount. It is possible to independently control a spectralcharacteristic represented by the transmittance and the phase shiftamount (phase angle).

On the other hand, with the miniaturization of an LSI pattern, it isexpected that the wavelength of the exposure light source (exposurewavelength) will be shortened from the existing KrF excimer laser (248nm) to the ArF excimer laser (193 nm) and further to the F₂ excimerlaser (157 nm) in future.

In the existing halftone phase shift mask, a film is typically designedso that the halftone phase shifter portion has an exposure lighttransmittance around 6%. However, in anticipation of a higherresolution, a higher transmittance is desired. In future, atransmittance of 15% or more will be required.

With the pursuit of the shortened wavelength of the exposure lightsource and the higher transmittance, the range of selection of amaterial of the halftone phase shifter portion which satisfies apredetermined transmittance and a predetermined phase shift amount tendsto be narrowed. Moreover, with the increase in transmittance, a materialhaving a high transmittance is required. Furthermore, with theshortening of the wavelength of the exposure light source, the materialhaving a high transmittance is necessary as compared with the wavelengthpreviously used. These requirements cause a problem that etchingselectivity with a quartz substrate during patterning is reduced.

In the halftone phase shifter portion of a multilayered structurecomprising two or more layers, a phase difference and a transmittancecan be controlled by a combination of multilayered or double-layerfilms. It is therefore easy to select the material. Furthermore, amaterial which serves as an etching stopper of an upper layer can beselected as a lower layer.

In the phase shift mask, a reflectance in the exposure light beam mustbe reduced to some extent. Generally, in a step of inspecting theappearance of the pattern, a light beam longer in wavelength than theexposure wavelength is used as an inspection wavelength and atransmission type defect inspection apparatus (e.g., KLA300 series, andthe like) is used. Therefore, if the transmittance is excessively high(e.g., 40% or more) with respect to the inspection wavelength (forexample, if the exposure wavelength is 248 nm (KrF excimer laser), theinspection wavelength is 488 nm or 364 nm), the inspection is difficultto perform.

Especially, with the shortened exposure wavelength, the halftone phaseshifter portion having a high transmittance is required as describedabove. However, the material having a high transmittance tends to belarge in increasing ratio of the transmittance with respect to thechange in wavelength towards a longer wavelength. Therefore, in thesingle-layer halftone phase shifter, it is further difficult to reducethe transmittance with respect to the inspection wavelength to apredetermined range.

Furthermore, in the defect inspection apparatus, development of a newinspection method using transmitted and reflected light beams has beenmade. If the inspection is carried out in this method, the transmittancein the inspection wavelength may be slightly high (e.g., 50 to 60%) ascompared with the inspection using the transmitted light. However, it isnecessary to control the reflectance in the inspection wavelength sothat the reflectance has some difference (e.g., 3% or more) from that ofa transparent substrate.

Under the above-mentioned situation, the use of the halftone phaseshifter portion of the multilayered type including two or more layersmakes it easy to control reflection and transmission characteristics inthe exposure and inspection light beams.

The double-layer halftone phase shift mask is described, for example, inJapanese Unexamined Patent Publication No. H4-136854 in which thehalftone phase shifter portion has a double-layer structure comprising athin Cr layer and a coating glass (Prior-art Example 1).

It is known that the halftone phase shifter portion of a multilayeredstructure can be prepared by the use of a single common apparatus and asingle common etchant for etching. For example, Japanese UnexaminedPatent Publication No. H6-83034 discloses a mask including a halftonephase shifter portion having a multilayered structure in which the sameelement is contained in a plurality of layers (e.g., a double-layerstructure comprising Si and SiN layers) (Prior-art Example 2).

Furthermore, the technique for reducing the transmittance with respectto the inspection wavelength is described in Japanese Unexamined PatentPublication No. H7-168343. Specifically, a double-layer structureincludes a single-layer film known as a single-layer type halftone phaseshifter, such as MoSiO or MoSiON, and a transmission film low inwavelength dependency of the transmittance in combination with thesingle-layer film. With this structure, a desired transmittance can beobtained with respect to both the exposure light beam (KrF excimerlaser) and the inspection light beam (488 nm) (Prior-art Example 3).

Furthermore, a mask having the phase shifter portion of a multilayeredstructure using a tantalum-silicide-based material is described inJapanese Unexamined Patent Publication No. 2001-174973. Specifically,the halftone phase shifter portion has a double-layer structure whichincludes an upper layer containing tantalum, silicon, and oxygen as maincomponents and a lower layer containing tantalum as a main component andnot containing silicon (Prior-art Example 4).

Furthermore, Japanese Unexamined Patent Publication No. 2001-337436discloses a mask including the halftone phase shifter portion having adouble-layer structure which includes an upper layer containingtantalum, silicon, and oxygen as main components and a lower layercontaining chromium and chromium-tantalum alloy as main components(Prior-art Example 5).

However, the above-described prior-art examples have the followingproblems.

Generally, a halftone phase shifter film is provided with a lightshielding Cr layer formed thereon. The light shielding Cr layer servesas an etching mask layer for the halftone phase shifter film and issubsequently used to form a light shielding portion at a desiredposition on the mask.

In the structure of coating glass/thin Cr layer/glass substrate as inthe Prior-art Example 1, the light shielding Cr layer is formed on thecoating glass. In this event, preparation is made of a mask pattern of athree-layer structure of light shielding Cr layer/coating glass/thin Crlayer with a resist pattern, generally used in patterning, transferredthereon. Thereafter, the light shielding Cr layer is selectively removedtypically by wet etching.

However, since the light shielding Cr layer is same in material with thethin Cr layer, there is a problem that the thin Cr layer is affected inthe selective removing process of the light shielding Cr layer.Specifically, the thin Cr layer is etched and the pattern is sometimescompletely removed in the principle similar to that of lift-off. Whenthe thin Cr layer is side-etched, the transmittance in the vicinity of apattern edge will inevitably be changed.

Next, in Prior-art Example 2, it is possible to continuously deposit,for example, the Si and the SiN layers by the use of the same sputteringapparatus and the same target of Si. However, if the SiN layer isdeposited by reactive sputtering using the Si target and a sputteringatmosphere containing nitrogen, poisoning of the target by the reactivesputtering is caused to occur. As a result, reproducibility cannot beattained and productivity is decreased. Furthermore, with the use ofSiN, the transmittance becomes excessively low with the shortening ofthe exposure wavelength in recent years.

Next, in Prior-art Example 3, MoSiO or MoSiON is used as the material ofthe single-layer film (upper layer). However, by inclusion of the metal,the transmittance is reduced. Therefore, this example is not suitablefor the recent shortening of the exposure wavelength. Moreover, if thecontent of the metal is reduced, the refractive index is reduced so thatthe film thickness of the halftone phase shifter increases. This isdisadvantageous for the fine processing.

Furthermore, in Prior-art Examples 4 and 5, TaSiO is used as thematerial of the upper layer. However, by inclusion of the metal, thetransmittance is reduced. Therefore, these examples are not suitable forthe recent shortening of the exposure wavelength. Moreover, if thecontent of the metal is reduced, the refractive index is reduced so thatthe film thickness of the halftone phase shifter increases. This isdisadvantageous for the fine processing.

Moreover, in these prior-art examples, the lower layer serves as anetching stopper against dry etching of the upper layer using afluorine-based gas. Thereafter, the lower layer is etched by dry etchingusing a chlorine-based gas.

However, the lower layer containing tantalum in the Prior-art Example 4has an insufficient etching selectivity with respect to thefluorine-based dry etching of the upper layer. In case of thechromium-tantalum alloy in the Prior-art Example 5, an etching rate withthe chlorine-based gas is slow and a high-accuracy pattern is notobtained.

SUMMARY OF THE INVENTION

It is therefore an object thereof to provide a halftone phase shift maskblank and a halftone phase shift mask superior in fine processabilityduring etching for forming a halftone phase shifter portion.

It is another object of the present invention to provide a halftonephase shift mask blank and a halftone phase shift mask which can be usedunder a high transmittance (transmittance of 8 to 30%) in case where anexposure light source is shortened in wavelength, especially, in anexposure wavelength region of 140 nm to 200 nm, specifically, in thevicinity of 157 nm as the wavelength of an F₂ excimer laser and in thevicinity of 193 nm as the wavelength of an ArF excimer laser.

According to the present invention, there is provided a halftone phaseshift mask blank in which a phase shifter film comprises a filmcontaining silicon, oxygen, and nitrogen as main components and anetching stopper film formed between the film and a transparentsubstrate.

In the present invention, in halftone phase shifter layers formed on thetransparent substrate, a film adjacent to the transparent substrate isreferred to as a lower layer and a film formed on the lower layer isreferred to as an upper layer.

Based on the facts that SiN_(x) has a high irradiation resistanceagainst the exposure light beam and a high chemical resistance against acleaning liquid or the like because Si—N bond contributes to densenessof a matrix of a film and that SiO_(x) has a relatively hightransmittance even on a short wavelength side, the present inventorshave focused their attention to SiO_(x)N_(y) which utilizes merits ofboth of these materials.

Furthermore, the present inventors have found out that, by controllingthe composition of SiO_(x)N_(y), it is possible to obtain a phaseshifter film suitable for use with the exposure light beam having ashort wavelength. Furthermore, the present inventors have found out thatthe halftone phase shifter film having a double-layer structure of anSiO_(x)N_(y) film (upper layer) and an etching stopper film (lowerlayer) is excellent not only in exposure light irradiation resistanceand chemical resistance but also in processability of a pattern.

Herein, the etching stopper film is a film made of a material having afunction of inhibiting the progress of etching of the SiO_(x)N_(y) film,having a function of facilitating detection of an etching end point ofthe phase shifter film, or having both of the above-mentioned functions.

The upper layer is made of a material substantially consisting ofsilicon, oxygen, and nitrogen. That is, the upper layer comprises a filmcontaining silicon, oxygen, and nitrogen as main components. Thismaterial is advantageous in the following respects. Specifically, evenif the exposure light beam has a shortened wavelength, a desiredtransmittance and a phase difference can be controllably achieved incombination with the lower layer. In addition, the irradiationresistance against the exposure light beam and the chemical resistanceagainst the cleaning liquid or the like are high. Furthermore, since arelatively high refractive index can be obtained, it is possible tosuppress the total film thickness of the halftone phase shifter filmsufficient to obtain a desired phase difference. Therefore, the fineprocessability of the halftone phase shifter film is superior.

For the above-mentioned material of the upper layer, it is preferable toadjust and control a complex refractive index real part n to a valuewithin a range of n≧1.7 and a complex refractive index imaginary part kto a value within a range of k≦0.450. These ranges are advantageous inachieving desired optical characteristics of the halftone phase shiftmask following the shortening of the wavelength of the exposure lightbeam. For the F₂ excimer laser, the range of k≦0.40 is preferable andthe range of 0.07≦k≦0.35 is more preferable.

For the ArF excimer laser, the range of 0.10≦k≦0.45 is preferable. Forthe F₂ excimer laser, the range of n≧2.0 is preferable and the range ofn≧2.2 is more preferable. For the ArF excimer laser, the range of n≧2.0is preferable and the range of n≧2.5 is more preferable.

In order to obtain the above-described optical characteristics, thecontents of the above-mentioned components are selected as follows. Thecontent of silicon is 35 to 45 atomic %, the content of oxygen is 1 to60 atomic %, and the content of nitrogen is 5 to 60 atomic %. If thecontent of silicon is greater than 45% or if the content of nitrogen isgreater than 60%, the transmittance of the film becomes insufficient.Conversely, if the content of nitrogen is less than 5% or if the contentof oxygen exceeds 60%, the transmittance of the film is too high and,therefore, the function of the halftone phase shifter film is lost. Ifthe content of silicon is less than 35% or if the content of nitrogenexceeds 60%, the structure of the film physically and chemically becomesvery unstable.

From the similar viewpoint, the contents of the above-mentionedcomponents are preferably selected as follows for the F₂ excimer laser.The content of silicon is 35 to 40 atomic %, the content of oxygen is 25to 60 atomic %, and the content of nitrogen is 5 to 35 atomic.Similarly, the contents of the above-mentioned components are preferablyselected as follows for the ArF excimer laser. The content of silicon is38 to 45 atomic %, the content of oxygen is 1 to 40 atomic %, and thecontent of nitrogen is 30 to 60 atomic %. In addition to theabove-mentioned components, a small amount of impurities (metal, carbon,fluorine, and the like) may also be contained.

The upper layer in the present invention can be deposited by reactivesputtering using a target substantially comprising silicon and asputtering atmosphere using a reactive gas containing a rare gas,nitrogen, and oxygen. The target substantially comprising silicon ishigh in number density and purity and is therefore stable as comparedwith the case where a mixed target such as metal silicide is used.Accordingly, there is an advantage that a particle generation ratio ofthe resultant film is reduced.

The etching stopper layer comprises a film made of a material having afunction of inhibiting the progress of etching of the SiO_(x)N_(y) film,having a function of facilitating detection of an etching end point ofthe phase shifter film, or having both of the above-mentioned functions.

Preferably, the film having a function of inhibiting the progress ofetching of the SiO_(x)N_(y) film is made of a material having a lowselectivity with respect to etching of the phase shifter layer, that is,a material having an etching rate lower than that of the SiO_(x)N_(y)film with respect to an etching medium used in etching of theSiO_(x)N_(y) film. Specifically, it is desired that the film is made ofa material which has an etching selectivity of 0.7 or less, preferably0.5 or less.

On the other hand, the latter etching stopper film having a function offacilitating detection of an etching end point of the phase shifter filmis a film made of a material in which the difference in reflectance foran etching end point detection light beam (e.g., 680 nm) between thetransparent substrate (e.g., the synthetic quartz substrate) and theetching stopper is greater than that between the transparent substrateand the SiO_(x)N_(y) film.

Preferably, the material has a refractive index (the real part of thecomplex refractive index) higher than those of the SiO_(x)N_(y) film andthe transparent substrate. Preferably, the etching stopper film is madeof a material in which the difference in refractive index for thewavelength of the etching end point detection light beam between theetching stopper film and the SiO_(x)N_(y) film is 0.5 or more,preferably 1 or more and in which the difference in refractive indexbetween the etching stopper film and the transparent substrate is 0.5 ormore, preferably 1 or more.

It is desired that the etching stopper layer has an etching selectivityof 1.5 or more, preferably 2.0 or more. Specifically, if the etchingstopper layer cannot be removed, the transmittance in a lighttransmitting portion decreases so that a contrast upon pattern transferis deteriorated. Even if the layer can be removed, the substrate mightbe etched in the vicinity of the etching end point unless the etchingrate of the etching stopper layer is greater than that of the substrate.As a result, the processing accuracy is deteriorated.

Taking the aforementioned respects into account, use is suitably made ofa single kind of material or two or more kinds of materials selectedfrom a group including magnesium, aluminum, titanium, vanadium,chromium, yttrium, zirconium, niobium, molybdenum, tin, lanthanum,tantalum, tungsten, silicon, and hafnium, as well as a compound (oxide,nitride, nitric oxide) thereof, and so on.

The etching stopper film preferably has a film thickness falling withina range of 10 to 200 angstroms. If the thickness is smaller than 10angstroms, etching cannot completely be inhibited and a significantchange in reflectance cannot be detected. This may results indegradation in pattern processing accuracy.

On the other hand, expansion of the pattern by the progress of isotropicetching may reach about twice the film thickness at maximum, dependingupon the etching process. Therefore, if the film thickness exceeds 200angstroms when a pattern line width of 0.1 μm (=1000 angstroms) or lessis processed, a dimensional error of 40% or more is produced. In thisevent, the quality of the mask is seriously adversely influenced.

Preferably, the etching stopper layer has a function of adjusting thetransmittance. The transmittance of the etching stopper layer itselfwith respect to the exposure wavelength (140 to 200 nm, around 157 nm,or around 193 nm) is selected between 3 and 40%. Thus, the transmittancein the phase shifter portion is maintained and the transmittance for theinspection wavelength longer than the exposure wavelength can be reducedby the etching stopper layer formed at a lower part of the phase shifterportion (by lamination of a different material).

Specifically, inspection of the mask in a manufacturing process ispresently carried out by the use of an inspection light beam having awavelength longer than the exposure wavelength and measuring thetransmitted light strength. The transmittance of a semi-transmittingportion (phase shifter portion) is preferably 40% or less within therange of 200 to 300 nm as the inspection wavelength presently used.Specifically, if the transmittance is 40% or more, a contrast from thetransmitting portion is not sufficient and an inspection accuracybecomes low. In case where the etching stopper film is made of amaterial having a high light shielding function, the etching stopperfilm may be made of a single kind of material or two or more kinds ofmaterials selected from a group including aluminum, titanium, vanadium,chromium, zirconium, niobium, molybdenum, lanthanum, tantalum, tungsten,silicon, and hafnium, as well as nitride thereof.

Preferably, the etching stopper layer has a film thickness sufficientlysmaller than that of the phase shifter portion. Specifically, a filmthickness of 200 angstroms or less is appropriate. If the thicknessexceeds 200 angstroms, it is highly possible that the transmittance atthe exposure wavelength is lower than 3%. In this case, the phase angleand the transmittance are adjusted by the two layers of the SiO_(x)N_(y)film and the etching stopper film.

Preferably, the transmittance of the etching stopper layer itself withrespect to the exposure wavelength (140 to 200 nm, around 157 nm, oraround 193 nm) is selected to be 3 to 40% and the transmittance isadjusted to be 3 to 40% when the etching stopper layer is laminated withthe SiO_(x)N_(y) film. In case where the etching stopper layer isprovided, the etching stopper layer exposed on the surface of a portioncorresponding to the light transmitting portion must be removable. Thisis because, if the light transmitting portion is covered with theetching stopper layer, the transmittance of the light transmittingportion decreases.

In order to remove the etching stopper film, use must be made of amethod different from etching of the SiO_(x)N_(y) film in case where theetching stopper film is made of a material having a function ofinhibiting the progress of etching of the SiO_(x)N_(y) film. In casewhere the etching stopper film is made of a material having a functionof facilitating detection of the etching end point of the phase shifterfilm, etching of the SiO_(x)N_(y) film and etching of the etchingstopper film may be carried out by the same method or by differentmethods.

The phase shifter film made of the SiO_(x)N_(y) film can be etched bydry etching (RIE: Reactive Ion Etching) using a fluorine-based gas suchas CHF₃, CF₄, SF₆, and C₂F₆ and a mixed gas thereof. On the other hand,in case where the etching stopper film is etched and removed in a methoddifferent from that for the phase shifter film, use may be made of dryetching using a fluorine-based gas different from that used in removingthe phase shifter film, dry etching using a chlorine-based gas such asCl₂ and Cl₂+O₂, or wet etching using acid, alkali, or the like.

As the etching stopper film removable by the fluorine-based dry etchingsame as the etching of the phase shifter film of the SiO_(x)N_(y) film,use may made of a material such as silicon, MoSi_(x), TaSi_(x), WS_(x),CrSi_(x), ZrSi_(x), and HfSi_(x).

In case where the etching stopper film which can be etched continuouslywith the SiO_(x)N_(y) film is provided as described above, the merit inthe manufacturing process is large. As the etching stopper film whichcan be etched by a method different from that of the etching of thephase shifter film comprising the SiO_(x)N_(y) film, use is preferablymade of a thin film containing Ta (for example, a thin film of Ta,TaN_(x), TaZr_(x), TaCr_(x), or TaHf_(x)), a thin film containing Zr, ora thin film containing Hf, which can be etched by dry etching using Cl₂.Alternatively, use may preferably be made of a thin film containing Crwhich can be etched by dry etching using Cl₂+O₂.

In case where the etching stopper film is made of the material having afunction of inhibiting the progress of etching of the SiO_(x)N_(y) filmand having a high transmittance, the etching stopper film may bedisposed between the transparent substrate and the lightsemi-transmitting film of the above-described halftone phase shift maskhaving a single-layer structure. In this structure, the etching stopperexposed on the light transmitting portion need not be removed.

The etching stopper layer is particularly effective in case where theSiO_(x)N_(y) film contains 40 atomic % or more oxygen or in case wherethe difference in refractive index from the transparent substrate is 0.5or less, preferably 0.3 or less.

Moreover, the present inventors have found out a predetermined materialfor the lower layer, which is resistant against the fluorine-based gasand which can be etched by dry etching using a gas (e.g., thechlorine-based gas) different from the fluorine-based gas in case wherethe upper layer is etched by dry etching using the fluorine-based gas.

First, the predetermined material may be a single metal selected from afirst group consisting of Al, Ga, Hf, Ti, V, and Zr or a material (analloy or any other mixture) containing two or more kinds of these metals(the material will hereinafter be referred to as a first material). Thesingle metal selected from the first group or the first material is amaterial which is resistant against the fluorine-based gas and which canbe etched by dry etching using a gas (e.g., a chlorine-based gas)different from the fluorine-based gas.

The single metal selected from the first group or the first material isa material which has a high etch resistance in the dry etching using thefluorine-based gas and which can easily be etched using the gas (e.g.,chlorine-based gas, bromine-based gas, iodine-based gas, or the like)different from the fluorine-based gas.

The lower layer is required to have a resistance against the dry etchingusing the fluorine-based gas to the extent that the effect as theetching stopper layer for the upper layer is obtained. The etching rateof the material of the lower layer is preferably between 0 and severaltens of angstroms/min, although it depends upon the thickness of thelower layer and the etching rate ratio (hereinafter referred to as theselectivity) with respect to the upper layer. Preferably, the materialcan be etched and removed in the dry etching of the lower layer usingthe chlorine-based gas to the extent allowable in a desired etchingprocess. It is desired that the material has an etching rate of fivetimes or more, more preferably ten times or more in terms of theselectivity with respect to the substrate material.

From a viewpoint of the high chemical resistance, Hf, Zr, or the like ispreferable as the single metal selected from the first group. From aviewpoint of easiness in preparing the sputtering target, Al, Ti, V, orthe like is preferable.

Secondly, the predetermined material may be a material (hereinafterreferred to as the second material) containing at least one kind ofmetal selected from a group consisting of Cr, Ge, Pd, Si, Ta, Nb, Sb,Pt, Au, Po, Mo, and W and at least one kind of metal selected from theabove-mentioned first group (Al, Ga, Hf, Ti, V, and Zr) (including analloy and any other mixture). By addition of a metal selected from thefirst group to the metal selected from the second group, theabove-mentioned material fully exhibits a resistance against thefluorine-based gas and can be etched by dry etching using a gas (e.g.,the chlorine-based gas, bromine-based gas, iodine-based gas, and thelike) different from the fluorine-based gas. Thus, the material canexhibit a function similar to that of the first material.

Herein, the metals specified in the second group (excluding Cr) isinferior in resistance against the fluorine-based gas to the metalspecified in the first group. In case where the metal selected from thefirst group is added, the resistance against the fluorine-based gas isimproved as compared with the case where the metal is not added.Furthermore, in case where the metal selected from the first group isadded, a desired resistance against the fluorine-based gas issufficiently exhibited. It is to be noted that Cr has a resistanceagainst the fluorine-based gas, which is equivalent to that of the metalspecified in the first group.

The metal specified in the second group is a material having an etchingrate for the chlorine-based gas which is equivalent to that of the metalin the first group or which is slightly inferior to such an extent thatcompensation is possible by addition of the first group. As describedabove, the metal specified in the first group is a material which caneasily be etched, for example, using the chlorine-based gas. Therefore,the material containing the metal specified in the second group and themetal specified in the first group added thereto is maintained orimproved in etching characteristic for the chlorine-based gas.

Thus, the present inventors have found out that the etchingcharacteristic with respect to the chlorine-based gas is maintained andthe resistance against the fluorine-based gas is remarkably improved byadding a small amount of the metal selected from the first group to themetal selected from the second group. The added amount of the metalselected from the first group with respect to the metal selected fromthe second group is selected to be 2% or more. If the added amount issmaller than 2%, the characteristic of the added material is not fullyexhibited and the effect of improving the resistance against thefluorine-based gas is insufficient.

Thirdly, the predetermined material may be a material containing thesingle metal, the first material, or the second material with nitrogenand/or carbon added thereto. Nitrogen and/or carbon is preferablycontained in a range such that the desired characteristic is notimpaired.

Herein, the fluorine-based gas may be C_(x)F_(y) (e.g., CF₄, C₂F₆),CHF₃, a mixture gas thereof, or any one of these gases with O₂ or a raregas (He, Ar, Xe) added as an additional gas.

Moreover, as a gas other than the fluorine-based gas, a halogen-basedgas other than fluorine (chlorine-based, bromine-based, iodine-based, ora mixture gas thereof) can be used. As the chlorine-based gas, use maybe made of Cl₂, BCl₃, HCl, a mixture gas thereof, or any one of thesegases with a rare gas (He, Ar, Xe) added as an additional gas.

As the bromine-based gas, use may be made of Br₂, HBr, a mixture gasthereof, or any one of these gases with a rare gas (He, Ar, Xe) added asan additional gas. As the iodine-based gas, use may be made of I₂, HI, amixture gas thereof, or any one of these gases with a rare gas (He, Ar,Xe) added as an additional gas.

Herein, it is preferable to use the chlorine-based gas as the gasdifferent from the fluorine-based gas, because the etching rate can beincreased as compared with the bromine-based gas or the iodine-basedgas. It is to be noted that a gas containing both fluorine and adifferent gas other than fluorine can also be used. In this case, one offluorine and the different gas which includes a greater ratio of excitedspecies in active species in plasma is preferentially referred to.

If the excited species of fluorine is greater in ratio, the gas isdefined as the fluorine-based gas. If the excited species of thedifferent gas (e.g., chlorine) other than the fluorine-based gas isgreater, the gas is defined as the different gas other than thefluorine-based gas (e.g., the chlorine-based gas). If fluorine and adifferent halogen element or elements are contained in a single gascomposition (e.g., ClF₃, and the like), the gas is defined as thefluorine-based gas.

For the gas other than the fluorine-based gas, it is preferable thatoxygen is not contained as the additional gas. This is because theaddition of oxygen may decrease the etching rate due to surfaceoxidation. For example, an etching gas Cl₂+O₂ typically used in etchingof Cr causes a complicated reaction, which tends to produce etchingdistribution. Therefore, it is preferable to perform the dry etching bya single-component gas such as Cl₂ so as to obtain a high-accuracypattern.

Next, the function of each layer which satisfies the above-describedrequirement will be described.

The lower layer has a resistance against the fluorine-based gas. Even ifthe upper layer is dry-etched using the fluorine-based gas and thesurface of the lower layer is exposed, film reduction of the lower layeris slow. Therefore, it is possible to set a sufficient over-etching timeof the upper layer, considering the removal of a residual film of theupper layer as a result of the etching distribution due to thedifference in density of the pattern. As a result, it is possible toform a pattern exactly reflecting a mask pattern and to improve thedimensional accuracy.

The lower layer is made of the material which can be etched by the dryetching using the gas (e.g., the chlorine-based gas) different from thefluorine-based gas (i.e., which has a certain degree of etching rate forthe chlorine-based gas). Therefore, the lower layer can be dry-etched,for example, using the chlorine-based gas. Even if the surface of thetransparent substrate is exposed, the surface layer of the transparentsubstrate is hardly etched or dug. Therefore, it is possible to avoidfluctuation in phase difference due to etching or digging of the surfacelayer of the substrate and variation in in-plane phase difference due tovariation in etching and to achieve high controllability of the phasedifference. This is because a quartz substrate often used as thesubstrate of the phase shift mask has a small etching rate with respectto the dry etching for removing the lower layer as compared with thematerial of the lower layer.

The etching rate of the lower layer with respect to the chlorine-basedgas is preferably as high as possible. Although depending upon therequired value of the CD dimensional accuracy and the etchingconditions, it is preferable that the etching rate is not smaller than2500 angstroms/min, 3000 angstroms/min, or 4000 angstroms/min.Specifically, the lower layer in the phase shift mask typically has anetching rate of 100 angstroms or less. Since the lower layer has a highetching rate, the etching of the lower layer comes to an end in severalseconds. An over-etching time is extremely short. An etching rate of 360angstroms/min corresponds to 6 angstroms/sec. Thus, an etched amount(removed amount) is extremely small.

Moreover, unlike the structure of the light shielding Cr layer/coatingglass/thin Cr layer/transparent substrate described in conjunction withthe prior art, the structure of the light shielding Cr layer/upperlayer/lower layer/transparent substrate according to the presentinvention is advantageous in the following respects. Since the lightshielding Cr layer is made of the material different from the materialof the lower layer, selective operation is possible in the process ofremoving the light shielding Cr layer. This removing process can beperformed not only by a wet process using a second ammonium solution ofcerium nitrate used in common but also may be carried out using the dryetching. Thus, it is possible to avoid an adverse influence as a resultof etching of the lower layer in the selective removing process of thelight shielding Cr layer, regardless of wet etching or dry etching. Thatis, the structure of this invention is adaptable to the above-mentionedprocess.

During deposition of each of the lower and the upper layers, depositionmay be carried out so that the film structure is an amorphous structureor a structure having extremely small grain boundaries. This contributesto the improvement of pattern accuracy. The reason is as follows. If thefilm structure is a columnar or a crystal structure, roughness(unevenness or irregularities) will be produced on a sidewall of thepattern during the etching. On the other hand, if the film structure isthe amorphous structure or the structure having extremely small grainboundaries, the sidewall of the pattern has a generally flat surface(substantially linear) during the etching.

If the film structure is the columnar or the crystal structure, filmstress may be generated to raise a problem. On the other hand, if thefilm structure is the amorphous structure or the structure having theextremely small grain boundaries, the film stress can easily becontrolled.

In case where the upper layer of the phase shifter film is made of aSi-based material such as SiO_(x), SiN_(x), SiO_(x)N_(y), SiC_(x),SiC_(x)N_(y), or SiC_(x)O_(y)N_(z), or a material containing theSi-based material and a metal M (for example, at least one of Mo, Ta, W,Cr, Zr, Hf) added thereto so that M/(Si+H)×100 is preferably 10 atomic %or less, the upper layer can easily be processed by the dry etchingusing the fluorine-based gas and has a high resistance against the dryetching using the chlorine-based gas. In case where the upper layer ismade of the above-mentioned material, it is possible to satisfy thepredetermined transmittance and the predetermined phase shift amount,even if the exposure wavelength is shortened to 193 nm as the wavelengthof the ArF excimer laser or 157 nm as the wavelength of the F₂ excimerlaser. Thus, it is possible to adapt to the shortened wavelength.

For example, the phase shift mask blank has a structure of SiO_(x) andSiO_(x)N_(y) layer/the lower layer of the predetermined material (thelayer having the above-described etching characteristic)/the transparentsubstrate. With this structure, the SiO_(x) and SiO_(x)N_(y) layer ispatterned by the dry etching using the fluorine-based gas and a portioncorresponding to the lower layer is processed by the dry etching usingthe chlorine-based gas so as to suppress the damage to an underlayer.

By the use of the blank having the above-mentioned structure, it ispossible to control the optical characteristic and to achieve the phaseshift effect even in a generation of the increasingly shortenedwavelength. Specifically, the phase shift amount is mainly controlled bythe thickness or the composition of the SiO_(x) and SiO_(x)N_(y) layeras the upper layer while the transmittance is mainly controlled by thethickness of the lower layer made of the above-described predeterminedmaterial. Thus, it is possible to control the optical characteristic.

By processing the lower layer by the dry etching using thechlorine-based gas, it is possible to prevent the transparent substrateas the underlayer from being damaged. Since the change in phase shiftamount by etching or digging of the transparent substrate can beavoided, the above-described optical characteristic can be controlled.As a consequence, a predetermined phase shift effect is achieved.

In the present invention, it is preferable to form the light shieldingCr layer on the phase shift mask blank, to form the resist pattern onthe shielding Cr layer to obtain a light shielding Cr pattern, and toetch the phase shifter film using a combination of the resist patternand the light shielding Cr pattern or the light shielding Cr patternalone as the mask. After etching the phase shifter film, the lightshielding Cr pattern is left in a light shielding band portion of anon-transfer region of the phase shift mask. Alternatively, the lightshielding Cr pattern is removed except an alignment mark forming portioninside and outside the transfer region or a desired region excluding theneighborhood of the boundary of the pattern, in addition to theabove-mentioned light shielding band portion. The light shielding Crlayer may be a single layer film or a multilayered film containing Cr orcontaining Cr, oxygen, carbon, and nitrogen.

In the present invention, the refractive index of the film of the upperlayer at the inspection wavelength is smaller than the refractive indexof the lower layer. In this condition, it is possible to adjust thereflectance to the inspection light beam. At the exposure wavelengthalso, the refractive index of the film of the upper layer is smallerthan the refractive index of the film of the lower layer. In thiscondition, it is possible to adjust the reflectance to the exposurelight beam so that the reflectance has a value smaller than a requiredvalue.

Specifically, in view of the pattern transfer, it is desired that thetransmittance for the exposure light beam is 3 to 20%, preferably 6 to20% while the reflectance for the exposure light beam is 30%, preferably20%. In view of the defect inspection of the mask using the transmittedlight beam, the inspection light transmittance is preferably 40% orless. In view of the defect inspection of the mask using the transmittedlight beam and the reflected light beam, it is preferable that theinspection light transmittance is 60% or less and the inspection lightreflectance is 12% or more.

As the exposure light beam upon using the halftone phase shift mask ofthe present invention, use is particularly made of an exposurewavelength region of 140 nm to 200 nm. Specifically, use may be made ofthe wavelength around 157 nm which is the wavelength of the F₂ excimerlaser and the wavelength around 193 nm which is the wavelength of theArF excimer laser. It is also possible to prepare a high-transmittanceproduct in which the halftone phase shifter portion has a hightransmittance (8 to 30%).

In the present invention, the film design is carried out so that theupper layer serves as a layer (phase adjustment layer) exhibiting afunction of mainly adjusting the phase shift amount while the lowerlayer serves a layer (transmittance adjustment layer) exhibiting afunction of mainly adjusting the transmittance.

Specifically, assuming that the phase shift amount of the exposure lightbeam passing through the upper layer (phase adjustment layer) and havinga wavelength λ is represented by φ (deg), the film thickness d of thephase adjustment layer is given by:d=(φ/360)×λ/(n−1)  (3),where n represents the refractive index of the phase adjustment layerwith respect to the light beam having the wavelength λ.

Assuming that the phase shift amount of the lower layer (transmittanceadjustment layer) is represented by φ′, the phase shift amount Φ of thehalftone phase shifter portion must be designed as follows:Φ=φ+φ′=180°The value of φ′ is generally falls in a range of −20°≦φ′≦20°. Beyond theabove-mentioned range, the film thickness of the lower layer is toolarge and the transmittance of the exposure light beam cannot beincreased. Therefore, the film thickness d of the upper layer isdesigned in the following range.0.44×λ/(n−1)≦d≦0.56×λ/(n−1)  (4)

Specifically, the film thickness of the lower layer may be 1 to 20 nm,preferably 1 to 15 nm. As a result, it is possible to reduce the filmthickness of the halftone phase shifter film to 120 nm or less, morepreferably to 100 nm or less.

It is to be noted that the phase shift amount of the halftone phaseshifter film is ideally 180° but, practically, the range of 180°±5° issufficient.

As the transparent substrate in the present invention, use may be madeof a synthetic quartz substrate. Particularly when the F₂ excimer laseris used as the exposure light beam, an F-doped synthetic quartzsubstrate, a calcium fluoride substrate, and the like can be used.

As the material of the lower layer, it is particularly preferable to usea material substantially consisting of tantalum and hafnium or amaterial substantially consisting of silicon and hafnium. The materialof the lower layer is resistant against the fluorine-based dry etchinggas and can be removed by the chlorine-based dry etching gas. With thisstructure, as a method (etching method) of processing the halftone phaseshifter film, the upper layer is etched by the dry etching using thefluorine-based gas while the lower layer is etched by the dry etchingusing the chlorine-based gas.

Specifically, tantalum or silicon, even in the form of a single metal,is a material which can be etched by the dry etching using thechlorine-based gas not damaging the transparent substrate. However,tantalum or silicon is not so superior in resistance against the dryetching of the upper layer using the fluorine-based gas.

On the other hand, the single metal of hafnium is a material which issuperior in resistance against the dry etching of the upper layer usingthe fluorine-based gas and which can be etched by the dry etching usingthe chlorine-based gas. If hafnium is added to tantalum or silicon, theresistance against the dry etching using the fluorine-based gas isimproved as compared with the case where hafnium is not added. Inaddition, the etching characteristic with respect to the chlorine-basedgas can be maintained or improved. Preferably, the amount of hafniumadded to tantalum or silicon is 2 atomic % or more from a viewpoint thatthe resistance against the fluorine-based dry etching gas is obtained.

In case where the lower layer is made of the material substantiallyconsisting of tantalum and hafnium or substantially consisting ofsilicon and hafnium, the added amount of hafnium contained in the lowerlayer is preferably 50 atomic % or less. This is because the lightsemi-transmitting film containing tantalum or silicon exhibits only asmall difference between the transmittance at the exposure wavelengthand the transmittance at the inspection wavelength. Alternatively, thisis because the transmittance at the inspection wavelength is greaterthan the transmittance at the exposure wavelength and such material issuitable in designing the optical characteristic (transmittance and/orreflectance of the exposure light and the inspection light). Therefore,inclusion of a sufficient amount of tantalum or silicon facilitates thedesign of the optical characteristic.

In the halftone phase shift mask blank and the halftone phase shift maskof the present invention, heat treatment or laser annealing may becarried out after deposition of the halftone phase shifter film. By theheat treatment, various effects, such as the relaxation of the filmstress, improvement of the chemical resistance and the irradiationresistance, and fine adjustment of the transmittance. The heat treatmenttemperature is preferably 200° C. or more, more preferably 380° C. ormore.

In the present invention, a light shielding film containing chromium asa main component may be formed on the halftone phase shifter film. Thelight shielding film is used as the etching mask layer for the halftonephase shifter film and is thereafter selectively removed to form a lightshielding portion at a desired position or in a desired area on thehalftone phase shift mask. As the light shielding film containingchromium as a main component, use may be made of a film having asingle-layer or a multilayered structure (including a film having acontinuous composition gradient) and containing chromium or containingoxygen, nitrogen, carbon, and/or fluorine in addition to chromium.Preferably, an antireflection film (antireflection at the exposurewavelength) containing oxygen is formed in a surface layer portion.

In case where the light shielding film containing chromium as a maincomponent is formed on the halftone phase shifter film of the halftonephase shift mask, the light shielding film can be formed as a lightshielding band to surround the transfer region. Alternatively, in orderto increase the contrast of a mark such as an alignment mark, a lightshielding film can be formed at a marking position. Alternatively, inorder to reduce a side lobe light beam while the phase shift effect isachieved, the light shielding film can be formed in a region except theneighborhood of the boundary of the light semi-transmitting portion.

The present invention includes an embodiment utilizing the dry etchingcharacteristic of the upper and the lower layers mentioned above andeliminating the restriction in vertical relationship and the restrictionin application. Thus, the present invention is applicable to a laminatematerial for dry etching (laminate material before dry etching) in theart, such as an etching mask material and an etching stopper material.

The demand for the material superior in dry etching characteristic isnot only restricted to the above-mentioned photo mask using the phaseshift but also reaches a wide range of application, for example, as theetching stopper layer intended to protect the underlayer and the etchingmask material required to have a high selectivity and a reducedthickness following miniaturization of the pattern.

In the above-mentioned embodiment, the second layer is made of amaterial (hereinafter referred to as a predetermined function exhibitingmaterial) which has a high etching resistance in the dry etching usingthe fluorine-based gas and which can easily be etched in a conditionusing the chlorine-based gas. The material of the second layer containsat least one of Al, Ga, Hf, Ti, V, and Zr. The above-mentionedpredetermined function is achieved by the film containing theabove-mentioned element or elements or the film containing another metaland the above-mentioned element added thereto. The amount of theabove-mentioned element or elements to another metal is 2% or more. Ifthe added amount is smaller than 2%, the characteristic of the addedmaterial is not fully exhibited and the above-mentioned predeterminedfunction is not achieved in the etching. As another metal describedherein, use may be made of a material which can be etched by thechlorine-based gas. For example, another metal may be Cr, Ge, Pd, Si,Ta, Nb, Sb, Pt, Au, Po, Mo, and W.

The use of the above-mentioned materials makes it possible to performhigh-selectivity etching utilizing the difference in dry etchingcharacteristic depending upon the species of the gas. This effect alsocontributes to reduction in thickness of the component layer (e.g.,reduction in thickness of the etching mask layer) and results in theimprovement in accuracy of the fine pattern.

During deposition of each of the first and the second layers, depositionmay be carried out so that the film structure is an amorphous structureor a structure having extremely small grain boundaries. This contributesto the improvement of pattern accuracy. The reason is as follows. If thefilm structure is a columnar or a crystal structure, roughness(unevenness or irregularities) will be produced on a sidewall of thepattern during the etching. On the other hand, if the film structure isthe amorphous structure or the structure having extremely small grainboundaries, the sidewall of the pattern has a generally flat surface(substantially linear) during the etching. If the film structure is thecolumnar or the crystal structure, film stress may be generated to raisea problem. On the other hand, if the film structure is the amorphousstructure or the structure having the extremely small grain boundaries,the film stress can easily be controlled.

The first layer in the above-mentioned embodiment also includes the casewhere an upper layer portion of the substrate corresponds to the firstlayer, i.e., the case where an etched pattern (a sinking or carvedpattern) is formed in a surface layer portion of the substrate with thesecond layer as an etching mask layer. The laminate in theabove-mentioned embodiment includes a laminate composed of the secondlayer and the substrate (the upper layer portion corresponds to thefirst layer).

BRIEF DESCRIPTION OF THE DRAWING

FIGS. 1A and 1B show sectional views of a halftone phase shift maskblank and a halftone phase shift mask according to an embodiment of thepresent invention, respectively;

FIGS. 2A through 2D are views for describing a sequence of steps ofprocessing each layer in Example 2;

FIGS. 3A through 3E are views for describing a sequence of steps ofprocessing each layer in Example 3;

FIGS. 4A through 4E are views for describing a sequence of steps ofprocessing each layer in Comparative Example 2;

FIGS. 5A through 5D are views for describing a first half of amanufacturing process of a halftone phase shift mask blank and ahalftone phase shift mask in each of Examples 5 through 10 andComparative Examples 3 through 5;

FIGS. 6A through 6D are views for describing a second half of themanufacturing process following the first half in FIGS. 5A through 5D;

FIG. 7 is a spectrum diagram of an optical characteristic of thehalftone phase shift mask blank in Example 5;

FIG. 8 is a spectrum diagram of the optical property of the halftonephase shift mask blank in Example 6; and

FIG. 9 is a view showing a modification of the halftone phase shift maskblank and the halftone phase shift mask according to the embodiment ofthe present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, the present invention will be described in detail inconjunction with several examples and comparative examples. It is notedhere that the present invention is not limited to the followingexamples.

Referring to FIG. 1A, a halftone phase shift mask blank 1 comprises atransparent substrate 2 and a halftone phase shifter film 5 formed onthe transparent substrate 2 and including a lower layer 3 and an upperlayer 4 formed on the lower layer 3.

Referring to FIG. 1B, a halftone phase shift mask 1′ comprises thetransparent substrate 2 and a halftone phase shifter portion 5′ formedon the transparent substrate 2 and including a lower layer portion 3′and an upper layer portion 4′ formed on the lower layer portion 3′. Withthis structure, a mask pattern 8 is formed which includes a lightsemi-transmitting portion 6 in which the halftone phase shifter portion5′ is formed and a light transmitting portion 7 in which the halftonephase shifter portion 5′ is not formed. Each of the halftone phaseshifter film 5 and the halftone phase shifter portion 5′ has a desiredtransmittance with respect to an exposure light beam and a phase shiftangle of about 180 degrees. Moreover, each of the halftone phase shifterfilm 5 and the halftone phase shifter portion 5′ is designed so that thetransmittance at an inspection wavelength or the transmittance and thereflectance fall within a desired range.

Example 1

Table 1 shows the result of confirming etching characteristics ofTaZr_(x) (representing the material containing Ta and Zr and not showingthe ratio of Ta and Zr: this also applies in the following) and Zr whendry etching using the fluorine-based gas or the chlorine-based gas wascarried out. Table 2 shows the result of confirming etchingcharacteristics of TaAl and TaHf when dry etching using thefluorine-based gas or the chlorine-based gas was carried out. Thus, inthis example, confirmation has mainly been made of the dry etchingcharacteristics of the film containing Ta as a main component and amaterial (Al, Hf, Zr) supposed to be related to the effect of thepresent invention.

TABLE 1 Zr content Etching rate Selection ratio (%) Etching gas (Å/min)(/QZ) TaZr_(x) Cl₂ 4020 11.2 Zr 100 Cl₂ 3370 9.4 QZ 0 Cl₂ 360 — TaZr_(x)1.8 C₂F₆ 40 0.3 TaZr_(x) 2.6 C₂F₆ 40 0.3 TaZr_(x) 4.3 C₂F₆ 10 0.1 Zr 100C₂F₆ 7 0.1 QZ 0 C₂F₆ 120 —

Each film material was deposited using the sputtering method. In orderto add the material, a metal piece of the material in consideration wasplaced on a Ta target. Then, deposition was carried out. Whether thematerial was added in the film was confirmed by the use of the X-rayphotoelectron spectroscopy (XPS). In the dry etching, those gases shownin Table 2 were used. In this example, the etching by a high-densityplasma was performed using an inductive coupling plasma source.

TABLE 2 Etching rate Selection ratio Etching gas (Å/min) (/QZ) TaAl Cl₂2880 11.5 TaHf Cl₂ 2980 11.0 QZ Cl₂ 260 — TaAl C₂F₆ 70 0.6 TaHf C₂F₆ 200.2 QZ C₂F₆ 110 —

As a result of the experiment, it has been confirmed that, by additionof a small amount of the materials (Al, Hf, Zr) according to the presentinvention, the resistance against the fluorine-based gas is improvedwhile a chlorine-based characteristic is maintained. It has beenconfirmed that the Zr single metal film according to the presentinvention is a material which has a high etching resistance (i.e., theetching rate is low) in the dry etching using the fluorine-based gas andwhich can easily be etched (i.e., the etching rate is high) in the dryetching using the chlorine-based gas

Comparative Example 1

In order to confirm the effect of addition in Example 1, confirmationwas made, in Comparative Example 1, of the dry etching characteristicrelated to the Ta single metal film without addition of theabove-mentioned materials. As shown in Table 3, the Ta single metal filmwas insufficient in selectivity with the quartz substrate with respectto the fluorine-based gas. The etching condition in this comparativeexample was similar to that in Example 1.

TABLE 3 Etching rate Selection ratio Etching gas (Å/min) (/QZ) Ta Cl₂2900 8.1 QZ Cl₂ 360 — Ta C₂F₆ 110 0.9 QZ C₂F₆ 120 —

Example 2

In this example, a SiON layer was processed with a Zr film used as anetching mask.

The film structure was resist/Zr/SiON (FIG. 2A). Each layer deposited onthe Si substrate was processed and the effect as the etching maskmaterial was confirmed. In this example, the film thickness of eachlayer was as follows. The Zr layer had a thickness of 200 angstroms andthe SiON layer had a thickness of 800 angstroms. After the Zr layer wasprocessed by the chlorine gas with the resist pattern as the mask (FIG.2B), the SiON layer was processed. Then, the residual film of the Zrlayer was measured. As a result, the residual film of 60% or more wasconfirmed. It has been revealed that the sufficient dry etchingresistance as the etching mask material was exhibited.

Example 3

In this example, preparation was made of a photo mask having a phaseshift effect. Herein, blanks having a structure of SiON/TaZr/QZsubstrate were finely processed taking the selectivity between thematerials into consideration.

For the two-layer film on the QZ substrate, RF magnetron sputtering wasperformed to deposit the SiON layer of about 800 angstroms and the TaZrlayer of about 60 angstroms. For patterning (or for formation of thelight shielding Cr layer), the Cr film of about 500 angstroms wasdeposited on the SiON layer. Thereafter, a ZEP resist for an electronbeam was applied. Through an electron beam drawing step and a developingstep, a test pattern having a width of 0.5 μm was formed (FIG. 3A).

Herein, the film thickness of each layer was selected with reference tothe phase difference of the light beam transmitted through the mask.

Based on the resist pattern, Cr processing was performed in a mixed gasof chlorine and oxygen (oxygen ratio of about 20%) (FIG. 3B).

Thereafter, the SiON layer was processed using a C₂F₆ gas (FIG. 3C).Then, the TaZr layer was etched by the chlorine gas (FIG. 3D). The Crlayer (including the resist film) was removed (or selectively removedleaving the light shielding band portion) by a wet process mainly usingthe cerium nitrate second ammonium solution (FIG. 3E). Thus, a desiredtest pattern was formed.

For patterning, the high-density plasma etching apparatus using theinductive coupling plasma source was used. The section of the processedpattern shape was observed by the use of a scanning electron microscope(SEM). As a result, formation of an excellent pattern without etching ordigging into the QZ substrate was confirmed.

For a sample in which processing was stopped when the SiON layer wasformed, pattern observation was similarly carried out. As a result, nosubstantial film reduction of the TaZr layer has been confirmed. Takingthe distribution into consideration, the over-etching time was added tothe predetermined dry etching time. In this manner, pattern formationwithout the residual film of the SiON layer was realized. Furthermore,side etching of the TaZr layer by the removal of the Cr layer was notrecognized.

Comparative Example 2

In this comparative example, the TaZr layer in Example 2 is replaced byTaN which is close in etching resistance for the fluorine-based gas tothe SiON layer. Except that the material on the QZ substrate waschanged, the processing similar to that of Example 3 was performed. TheTaN film was deposited by the reactive sputtering using a mixed gas ofargon and nitrogen. Specifically, processing of Cr was performed basedon the resist pattern (FIGS. 4A and 4B). Thereafter, the SiON layer wasprocessed using the C₂F₆ gas (FIG. 4C). Then, the TaN layer was etchedby the chlorine gas (FIG. 4D). The Cr layer (including the resist film)was removed by the wet process mainly using the cerium nitrate secondammonium solution (FIG. 4E). Thus, the predetermined test pattern wasformed.

In the manner similar to Example 2, the 0.5 μm test pattern was formed.As a result, an excellent shape of the pattern was obtained like in theforegoing example. However, etching or digging into the underlying QZsubstrate was confirmed. The etching rate of the TaN film by thefluorine-based gas was substantially equivalent to that of QZ.

Example 4

In this example, processing similar to that in Example 2 was performedexcept that the TaZr layer was replaced by the Hf layer and the Zrlayer.

In the similar manner, a fine pattern was formed and the pattern shapewas observed by SEM. As a result, it has been confirmed that the patternsimilar in level to that of Example 3 was formed. No substantialdifference was observed for the damage of the QZ substrate. It has beenconfirmed that excellent pattern formation was carried out.

Examples 5-10 & Comparative Examples 3-5

In Examples 5 to 7, 10 and Comparative Examples 3 to 5, the phase shiftmask blank and the phase shift mask were prepared using the F₂ excimerlaser (wavelength of 157 nm) for the exposure light beam and the lightbeam having a wavelength of 257 nm as the inspection light beam. InExamples 8 and 9, the phase shift mask blank and the phase shift maskwere prepared using the ArF excimer laser (wavelength of 193 nm) for theexposure light beam and the light beam having a wavelength of 364 nm asthe inspection light beam.

Next referring to FIGS. 5A to 5D and 6A to 6D, description will be madeof a manufacturing process of the present invention.

First, the lower layer 3 was deposited on the transparent substrate 2 ofsynthetic quartz by the use of the DC magnetron sputtering apparatuswith the target having the composition shown in Table 4 (in ComparativeExamples 3 and 5, single elements of tantalum and silicon, respectively)and the rare gas (argon gas) as a sputtering gas.

Next, by the use of the DC magnetron sputtering apparatus, the SiON filmas the upper layer 4 was deposited on the lower layer 3 by the reactivesputtering method using Si as the target and Ar, O₂, and N₂ as thesputtering gas (FIG. 5A).

Next, the halftone phase shift mask blank obtained as described abovewas heat-treated at 400° C. for one hour.

Thereafter, a light shielding film 9 containing chromium as a maincomponent and an electron beam drawing resist 10 were successivelylaminated on the two-layer film mentioned above (FIG. 5B). Then, patternwas drawn on the resist by the electron beam, followed by development bydipping and baking. Thus, a resist pattern 10′ was formed (FIG. 5C).

Subsequently, with the resist pattern used as a mask, a light shieldingband film pattern 9′ was formed by the dry etching using a Cl₂+O₂ gas.After changing the gas, the pattern of the halftone phase shifterportion was formed. In this step, CH₄+O₂ was used to etch the upperlayer 4 and the Cl₂ gas was used to etch the lower layer 3 (FIG. 5D). InComparative Example 3, however, the lower layer was also etched byCH₄+O₂ and, therefore, etching using Cl₂ gas was not performed.

Next, the resist on the resultant pattern was peeled off and removed(FIG. 6A). Again, the whole surface was coated with a resist 11 (FIG.6B). Thereafter, through a laser drawing and development process, aresist pattern 11′ was formed (FIG. 6C). Subsequently, a light shieldingband 12 was formed by the wet etching in a non-transfer region except atransfer region 1. Next, the resist pattern was peeled of and removed.Thus, the halftone phase shift mask was obtained (FIG. 6D).

The material of the transparent substrate, the composition of the upperlayer, the film thickness, the optical characteristics of the exposurelight beam and the inspection light beam, the etching characteristics,and the like are shown in Tables 4 to 7. The composition of the lowerlayer is substantially same as that of the target.

FIGS. 7 and 8 show transmittance and reflectance curves with respect tothe wavelengths in Examples 5 and 6, respectively. In Examples 5 and 6,for the transmittances with respect to the exposure light beam (F₂excimer laser) a standard product (6%) and a high-transmittance product(around 9%) were realized. The reflectance for the exposure light beamwas low and satisfied a required range (20% or less). The transmittancefor the inspection light beam was also lower than an upper limit of therequired value (40% or less). Thus, these examples were sufficientlyadapted for the inspection.

TABLE 4 Inspec- Inspec- Exposure Exposure tion tion wave- wave- Inspec-wave- wave- Upper layer Lower layer Exposure length length tion lengthlength Upper film thick- film thick- wave- trans- reflec- wave- trans-reflec- Transparent layer ness Lower layer ness length mittance tancelength mittance tance substrate material (Å) material (Å) (nm) (%) (%)(nm) (%) (%) Example 5 F doped SiON{circle around (1)} 790 Ta—Hf{circlearound (1)} 100 157 6.20 15.60 257 19.91 32.79 synthetic quartz 6 CaF₂SiON{circle around (1)} 800 Ta—Hf{circle around (1)} 65 157 9.14 13.55257 32.39 24.78 7 F doped SiON{circle around (1)} 810 Ta—Hf{circlearound (2)} 35 157 14.0 12.00 257 49.30 16.80 synthetic quartz 8Synthetic SiON{circle around (2)} 740 Ta—Hf{circle around (1)} 75 19315.1 17.00 364 30.40 21.50 quartz 9 Synthetic SiON{circle around (4)}960 Hf—Si 100 193 15.83 18.58 364 19.6 38.89 quartz 10 CaF₂ SiON{circlearound (3)} 920 Hf—Si 40 157 11.35 9.28 257 46.58 17.83 Compara- 3 Fdoped SiON{circle around (4)} 770 Ta 60 157 7.33 14.37 257 35.4 24.06tive- synthetic Example quartz 4 F doped SiON{circle around (3)} 807TaCr 80 157 6.30 18.20 257 29.40 25.13 synthetic quartz 5 F dopedSiON{circle around (4)} 790 Si 40 157 9.76 11.95 257 43.4 16.93synthetic quartz

TABLE 5 Composition 157 nm 193 nm (atomic %) SiON n k n k Si O N 2.000.20 — — 36 48 16 SiON — — 2.22 0.18 40 27 33 SiON 2.05 0.22 — — 36 4618 SiON 2.17 0.30 2.05 0.10 38 38 24

TABLE 6 Ta Hf Si Cr Zr Ta—Hf 90 10 Ta—Hf 80 20 Hf—Si 17 83 Ta—Cr 96 4

TABLE 7 Etching selection ratio Etching selection of lower layer toupper ratio of lower layer to layer substrate (SF₆ + He) (Cl₂) Example 50.25 >5 6 0.25 >5 7 0.08 >5 8 0.25 >5 9 0.17 >5 10 0.17 >5 Comparative 30.67 >5 Example 4 0.25 2.50 5 8.08 —

In Example 7, high transmittance (around 15%) with respect to theexposure light beam (F₂ excimer laser) was realized. The reflectance ofthe exposure wavelength was low and satisfied the required range (20% orless). The transmittance for the inspection wavelength was slightlyhigh. However, this example satisfied the required values (transmittanceof 60% or less, reflectance of 10% or more) required to perform theinspection using the transmitted light beam and the reflected lightbeam. Thus this example was sufficiently adapted for the inspectionusing the transmitted light beam and the reflected light beam.

In Example 8, high transmittance (around 15%) was realized. Thereflectance for the exposure wavelength was low and satisfied therequired range (20% or less). The transmittance for the inspection lightbeam was also lower than the upper limit of the required value (40% orless). Thus, this example was sufficiently adapted for the inspection.

In Examples 9 and 10, TaHf as the material of the lower layer inExamples 5 to 8 was replaced by HfSi. In Example 9, high transmittance(around 15%) with respect to the exposure light beam (ArF excimer laser)was realized. In Example 10, a high-transmittance product (around 11%)with respect to the exposure light beam (F₂ excimer laser) was realized.The reflectance of the exposure wavelength was low and satisfied therequired range (30% or less). The transmittance for the inspection lightbeam was also lower than the upper limit of the required value (40% orless). Thus, these examples were sufficiently adapted for theinspection.

In any one of Examples 5 to 10 described above, the lower layer is smallin etching selectivity with respect to an SF₆+He dry etching gas ascompared with the upper layer. Furthermore, the lower layer exhibits asufficient resistance against the etching of the upper layer. The lowerlayer has a large etching selectivity with respect to a Cl₂ dry etchinggas as compared with the transparent substrate. Thus, the damage uponthe transparent substrate during removal of the lower layer issuppressed. Therefore, it was possible to form the halftone phase shiftmask which was extremely excellent in sectional shape and minimized inchange of the optical characteristic due to over-etching of thetransparent substrate.

In Comparative Examples 3 and 5, single elements of tantalum and siliconwere used as the material of the lower layer without containing hafnium,respectively. In these comparative examples, the lower layer has a largeetching selectivity for the CH₄+O₂ dry etching gas as compared with theupper layer. Furthermore, even if the upper layer is dry etched usingthe fluorine-based gas and the surface of the lower layer is exposed,film reduction of the lower layer is fast. As a result, it is difficultto determine a sufficient over-etching time considering the removal ofthe residual film of the upper layer due to the etching distributioncaused by the difference in density of the pattern.

Thus, if the sufficient over-etching is not performed, the patternhaving an excellent sectional shape cannot be formed. If the sufficientover-etching is performed, the lower layer is also etched and thetransparent substrate is also dug so that the optical characteristicinevitably changes.

In Comparative Example 1, the sufficient over-etching of the upper layerwas not performed. As a result, the pattern having an excellentsectional shape was not obtained. In Comparative Example 3, the lowerlayer has a very large etching selectivity with respect to the CH₄+O₂dry etching gas as compared with the upper layer. As a result of thesufficient over-etching of the upper layer, the transparent substratewas also dug, and the phase shift amount inevitably changed.

In Comparative Example 2, the etching selectivity with respect to theCl₂ dry etching gas was small. Therefore, the damage upon the substratewas heavy during removal of the lower layer and the opticalcharacteristic was inevitably changed.

Referring to FIG. 9, the light shielding film is formed on the halftonephase shifter portion of the halftone phase shift mask in a differentmanner. Specifically, a light shielding layer 13 is formed in a desiredregion except in the vicinity of the boundary between the lightsemi-transmitting portion 6 and the light transmitting portion 7. Byforming the shielding layer 13 in the above-mentioned manner, the phaseshift effect is obtained and a side robe light beam can be reduced. Incase where the transmittance of the halftone phase shifter portion ishigh, an influence of the side robe light beam is problematic.Therefore, the above-mentioned structure is effective especially for thehigh-transmittance product (transmittance of the halftone phase shifterportion is 8 to 30%).

According to the present invention, it is possible to obtain a halftonephase shift mask blank and a halftone phase shift mask superior in fineworkability during etching for forming a halftone phase shifter portion.

With an exposure light source having a shortened wavelength, especiallyin an exposure wavelength region of 140 nm to 200 nm, ahigh-transmittance product (transmittance of 8 to 30%) at the wavelengtharound 157 nm as the wavelength of an F₂ excimer laser and around 193 nmas the wavelength of an ArF excimer laser is usable.

As a result, by the use of the halftone phase shift mask of the presentinvention, a high-accuracy transfer pattern can be transferred.

1. A halftone phase shift mask blank for use in manufacturing a halftonephase shift mask comprising a transparent substrate, a lighttransmitting portion formed on the substrate for transmitting anexposure light beam, a phase shifter portion formed on the substrate fortransmitting a part of the exposure light beam as a transmitted lightbeam and for shifting a phase of the transmitted light beam by apredetermined amount, the halftone phase shift mask being designed sothat light beams passing through the light transmitting portion andthrough the phase shifter portion cancel each other in the vicinity of aboundary portion therebetween, thereby keeping a predetermined contrastat a boundary portion of an exposure pattern to be transferred onto thesurface of an object to be exposed, wherein: the halftone phase shiftmask blank comprises a phase shifter film for forming the phase shifterportion on the transparent substrate; the phase shifter film comprisesan upper layer made of a material substantially consisting of silicon,oxygen, and nitrogen and a lower layer made of a material substantiallyconsisting of tantalum and hafnium.
 2. The halftone phase shift maskblank according to claim 1, wherein: the content of hafnium in the lowerlayer is in a range of 2 to 50 atomic % or more.
 3. The halftone phaseshift mask blank according to claim 1, wherein: the upper layer made ofthe material substantially consisting of silicon, oxygen, and nitrogencontains 35 to 45% silicon, 1 to 60% oxygen, and 5 to 60% nitrogen inatomic percentage.
 4. A halftone phase shift mask comprising atransparent substrate having a mask pattern formed thereon and includinga light transmitting portion and a light semi-transmitting portion, themask pattern being formed by etching the phase shifter film in thehalftone phase shift mask blank according to claim
 1. 5. A method ofmanufacturing the halftone phase shift mask according to claim 4,comprising the steps of: etching the upper layer by dry etching using afluorine-based gas, and etching the lower layer by dry etching using achlorine-based gas.